1. Field of the Invention
The invention relates to a process for producing hot-seal packs by welding, in particular for transdermal therapeutic systems (TTSs), and to a tool for carrying out the process.
2. Description of Prior Art
A known method for producing hot-seal packs for TTSs is to use two laps of packaging laminates, each composed of two or more layers, for example each composed of a layer of paper, of aluminium, and of weldable polymer, such as HDPE (high density polyethylene), Barex (PAN, polyacrylonitrile) or Surlyn (ethylene copolymer), and to bond these laps to one another at predetermined edges and/or lines by means of a heated sealing head while their polymer layers are lying against one another. To this end, the sealing head is pressed onto the laps to be bonded, and these are heated until under this head they exceed the melting point of the polymer layers, which therefore melt and enter into a cohesive bond with one another. This process can also be carried out using heated sealing heads arranged in opposite positions, and these may have the same or different temperatures, in order to accelerate the penetration of heat into the laps lying against one another. For example, the temperatures of each of two sealing heads may be 200xc2x0 C. in the case of packaging laminate with a polymer layer made from Barex with a melting point of 177xc2x0 C., and the temperature of one sealing head may be 200xc2x0 C. and that of the other may be 70xc2x0 C. in the case of a packaging laminate with a polymer layer made from HDPE with a melting point of 138xc2x0 C.
In this welding process, since the sealing tool temperature is considerably higher than the melting point, there can be blistering due to evaporation of moisture in the region of the welding zone (Barex), or else there can be excessive pinching of the melted polymer (HDPE) as a result of the necessary but excessive pressure exerted by the sealing tool, and there can also be damage to the pack material, giving defective and incomplete welded seams.
The quality of the welded seams can be improved by lowering the sealing-tool temperatures and the sealing-tool pressure while increasing the sealing periodxe2x80x94the residence time of the sealing tool on the pack material. However, this would also imply reducing the cycle rate of the welding machine, and this reduction would cause an undesirable reduction in the output of hot-seal packs.
The object of the invention is to provide a welding process for producing hot-seal packs, in particular for transdermal therapeutic systems, by transporting, in a predetermined cycle through a sealing unit, two laps of continuous pack material composed of two or more layers each having a weldable polymer layer lying against the other lap, and, using a sealing tool which acts upon both laps, in order to produce a weld along predetermined lines, bringing the laps into contact with pressure and with a temperature of above the melting point of the polymer, for a sealing period, which can improve the quality of the welded seams while the cycle rate of the welding machine remains the same, and to provide a sealing tool for carrying out the process.
This object is achieved in the welding process for producing hot-seal packs, in particular for transdermal therapeutic systems, as described above such that while the cycle remains the same there is an increase in the sealing period by a factor, in particular a factor of two, and in that there is a lowering of the temperature of the heated sealing heads of the sealing tool such that there is a considerable reduction in the temperature reached within the pack material, this temperature then being only slightly above the melting point of the polymer layer and using a sealing unit with heated sealing tools and a transport device for the pack material, characterized in that the sealing unit comprises two cooperating, heated sealing heads, said second sealing head being arranged or configured on the side of the pack material facing away from the first sealing head, and said sealing heads having, in succession in the direction of advance, two or more identical contact area structures corresponding to the predetermined weld lines for transmitting temperature and pressure to the pack material, with the length of one contact area structure in the direction of advance corresponding to the advancement cycle.
The invention envisages an increase in the sealing period, i.e. an increase by a factor deriving from the cycle. For simplicity, the specific case of xe2x80x9cdoublingxe2x80x9d is referred to hereinafter. For the purposes of the invention, the term xe2x80x9cdoublingxe2x80x9d includes increases by other factors.
According to the invention, use is made of a known process, by transporting, in a predetermined cycle through a sealing unit, two laps of continuous pack material composed of two or more layers and in each case having a weldable polymer layer lying against the other lap, and, using a sealing tool there which acts upon one lap or a sealing tool which acts upon both laps, in order to produce a weld along predetermined lines, bringing the laps into contact with pressure and with a temperature of above the melting point of the polymer, for a sealing period and according to the invention doubling the sealing period without altering the cycle or the output, and by lowering the temperature of the sealing tool so that there is a considerable reduction in the temperature reached within the pack material, this temperature then being only slightly above the melting point of the polymer layer. This very substantially prevents blistering due to evaporation of moisture in the region of the welding zone, and thus considerably improves the quality of the welded seams.
In parallel with this, it is also possible to lower the pressure exerted by the sealing tool, thus avoiding excessive pinching of molten polymer and also avoiding damage to the pack material.
In order to increase the sealing period by a factor, in a particular a factor of two, the pack material, after being first brought into contact with pressure and with heat, may be advanced in the cycle, along the predetermined lines, go and brought into contact on a second occasion or on further occasions with pressure and with heat, using the same period, during the period in which the subsequent sealed-bag pack is first being brought into contact with pressure and with heat.
To carry out the process, a sealing tool has been developed which has, in succession in the direction of advance, two or more, preferably two, identical contact area structures corresponding to the predetermined weld lines, for placing onto the pack material in order to transfer pressure and heat. The length of one contact area structure in the direction of advance therefore corresponds to the advancement cycle, and therefore, immediately after the advancement cyclexe2x80x94and thus essentially without delay or coolingxe2x80x94the pack material which has been brought into contact with the first contact area structure by means of the sealing tool is brought into contact on a second occasion or on further occasions with heat and with pressure at the same locations, signifying an increase in the sealing period by a factor, in particular a factor of two.
This sealing tool can therefore work together with a second sealing tool which has the same contact area structure and which has been arranged or designed on that side of the pack material facing away from the first sealing tool.